Display device and manufacturing method thereof

ABSTRACT

The present invention is to reduce display unevenness in a display device caused by dispersion of energy density of a laser beam. It is difficult for a periodical pattern to be recognized as display unevenness in display image. The display device of the present invention can visually reduce the display unevenness in the display image by utilizing the visual advantage described above. The display device can be manufactured using a TFT array substrate in which electric characteristic of plural TFTs arranged in a line in the minor axis direction of an linear shaped laser beam periodically fluctuates depending on the place in which each TFT is formed.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a means for reducing displayunevenness, and more specifically, the present invention relates to adisplay device given a reduction measure of display unevenness caused bydispersion of energy density of a laser beam, and a manufacturing methodthereof.

2. Description of the Related Art

A thin film transistor (hereinafter referred to as a TFT) is used as anelement for driving a liquid crystal display device, EL(ElectroLuminescence)display device and the like. A glass substrate has beenutilized for the purpose of manufacturing TFTs at low cost. It isdifficult to manufacture a TFT in a way that requires a long time heattreatment at approximately equal to or more than 600° C. Thus, atechnique for manufacturing a TFT in a low temperature process of atmost 600° C. for highest temperature in the process has been developed.A crystallization method using a laser beam is generally utilized for amethod for manufacturing a crystalline semiconductor film by such a lowtemperature process.

When dispersion of energy density of a laser beam due to instability ofoutput in a laser oscillator is caused in a method for manufacturing acrystalline semiconductor film using a laser beam, hereby, film qualityof the crystalline semiconductor film is also varied. It is know thatdispersion of a TFT electrical characteristic is generated by thecrystalline dispersion of the crystalline semiconductor film.Specifically, when an electrical characteristic of a TFT for driving apixel is varied, brightness unevenness or display unevenness such asgradation unevenness is caused in a display image.

Accordingly, two laser oscillators are used alternatively, for example,maintenance is performed to the one oscillator while performingcrystallization using one oscillator so as to obtain stable output fromthe laser oscillators all the time, then, an attempt to reduce filmquality dispersion of crystalline semiconductor film due to dispersionof energy density of a laser beam has been performed. (For example, U.S.Pat. No. 3,135,643)

In the case of using the above-described method, there is an effect thatthe process is not required to be interrupted for the maintenance.However, the frequency of maintenance itself can not be reduced. Thus,the development for a method in which trouble involved in maintenance orthe like is reduced, energy dispersion of a laser beam is reduced withmore convenient method, and more satisfactory display image is obtainedis required.

SUMMARY OF THE INVENTION

In view of the above-described problems, it is an object of the presentinvention to provide a display device in which display unevenness indisplay image can be visually reduced by utilizing a visual advantagethat a periodical pattern is difficult to be visually recognized asdisplay unevenness, and a manufacturing method thereof.

A display device of the present invention comprising a TFT arraysubstrate over which plural TFTs are arranged has a characteristic thatelectrical characteristic corresponding to the same electrical signal ofplural TFTs arranged in a line in at least one direction of columns orrows periodically fluctuates depending on the place in which each TFT isformed.

Note that the electrical characteristic is the one such as on currentvalue or threshold value which are obtained when the same electricsignal is applied to each TFT. Here, the on current value refers tocurrent value in a saturation region, especially in VD-IDcharacteristic.

The display device is the one in which a light emitting element isprovided; the luminescence brightness of a light emitting elementperiodically varies depending on the on current value of each TFT fordriving a light emitting element.

The brightness variation of periodical luminescence appears as aperiodical stripe pattern or a periodical lattice pattern in displayimage.

The periodical stripe pattern occurs in the case that the electricalcharacteristic under the same electrical signal of plural TFTs which arearranged in a line in at least one direction of columns or rowsperiodically fluctuates depending on the place in which each TFT isformed. In addition, the periodical lattice pattern occurs in the casethat the electrical characteristic in response to the same signal ofplural TFTs arranged in a line to the both directions of columns or rowsperiodically fluctuates depending on the place in which each TFT isformed.

Generally, the periodical pattern is difficult to be recognized asdisorder of a display image. Meanwhile, a random striped pattern iseasily identified as disorder of a display image.

The display device with which a semiconductor device of the presentinvention is provided can intentionally generate a periodical pattern.It becomes possible for brightness unevenness and the like caused inrandom stripped pattern to be hardly recognized as display unevenness.

In specific, the present invention has an effect of visually reducingbrightness unevenness in a display image caused by energy dispersion ofa laser beam.

A semiconductor device of the present invention comprising a TFT arraysubstrate over which plural TFTs are arranged has a characteristic thatfilm quality of a semiconductor film constituting plural TFTs arrangedin a line in at least one direction of columns or rows periodicallyfluctuates depending on the place in which each TFT is formed.

In case that film quality of semiconductor films varies, an electricalcharacteristic of TFTs also varies when the same electric signal isapplied thereto. Therefore, the electrical characteristic of plural TFTsarranged in one direction fluctuates periodically when the film qualityof a semiconductor film constituting plural TFTs arranged in onedirection fluctuates periodically.

A method for manufacturing a semiconductor device of the presentinvention is to manufacture a TFT by using a crystalline semiconductorfilm in which regions each having various film quality are formedperiodically and repeatedly.

A crystalline semiconductor film in which regions having various filmquality are repeatedly and periodically formed can be formed by forminga crystalline semiconductor film in which irradiation frequency of laserbeams is periodically varied in each region.

A crystalline semiconductor film in which irradiation frequency of laserbeams is periodically varied in each region thereof is formed by thefollowing processes. A second semiconductor regions having pluralcrystalline regions are formed by irradiating a first semiconductor filmwith a first laser beam so that the plural crystalline regions areformed at periodical intervals. And, a third semiconductor film isformed by irradiating a whole area of the second semiconductor film witha second laser beam.

Namely, a first region irradiated with the first and second laser beamsand a second region irradiated with only the second laser beam arerepeatedly and periodically formed in the third semiconductor film. Itis noted that the crystalline region formed by irradiating the firstlaser beam is irradiated “n” number times at a given point. Also, thewhole semiconductor film is irradiated with the second laser beam “m”number of times at a given point. Therefore, the first region isirradiated “n+m” number of times with laser beams and the second regionis irradiated “m” number of times with laser beams. The n and the m areoptional natural numbers. In addition, the order of the processes forirradiating with the first laser beam and for irradiating with thesecond laser beam is in random order. Not only irradiation frequency butalso energy density of a laser beam is changed in order to control thefilm quality of the crystalline semiconductor film.

BRIEF DESCRIPTION OF THE DRAWINGS

The patent or application file contains at least one drawing executed incolor. Copies of this patent or patent application publication withcolor drawing(s) will be provided by the Office upon request and paymentof the necessary fee.

FIGS. 1A to 1D are diagrams showing a method for manufacturing asemiconductor device of the present invention;

FIG. 2 is a diagram showing a method for manufacturing a semiconductordevice of the present invention;

FIGS. 3A to 3C are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 4A to 4C are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 5A to 5C are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 6A to 6C are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 7A and 7B are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 8A and 8B are diagrams showing a method for manufacturing asemiconductor device of the present invention, and a method formanufacturing a display device using the semiconductor device;

FIGS. 9A and 9B are display devices using a semiconductor device of thepresent invention;

FIGS. 10A and 10B are a photograph and a pattern diagram for comparingthe difference of the surface conditions of the semiconductor films,each of which is irradiated by different laser irradiation methods;

FIGS. 11A and 11B are photographs for comparing a display image in adisplay device of the present invention with a display image in displaydevice manufactured by the conventional technique;

FIG. 12 is a graph showing relation between irradiation frequency oflaser beams and dispersion of irradiation energy density;

FIG. 13 is a graph showing on current of TFT dependence on the TFT'sformation position;

FIGS. 14A to 14F are diagrams showing an example of electronicapparatuses applying the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Embodiment ModeEmbodiment Mode 1

A method for manufacturing a display device of the present invention isdescribed with reference to FIG. 1A to 1D and FIG. 2. A display deviceof the present invention can visually reduce display unevenness indisplay image by utilizing a visual advantage that a periodical patternis difficult to be visually recognized as display unevenness.Especially, a display device of the present invention has a moreadvantage in the case of displaying a whole image with single brightnessand a mono color (namely, under the same electric signal.)

In the present embodiment mode, a first and a second laser beams arepulsed laser beams formed in a linear shape. And the same laser mediumand the same oscillatory frequency are used respectively. When eitherlaser beam is used for irradiation, the position irradiated with a laserbeam is changed by fixing the laser beam itself without scanning it andmoving a stage on which a substrate 501 is mounted. The overlap ratio[%] between the region irradiated with a laser beam for “n” number oftimes and the region irradiated with a laser beam for “n+1” number oftimes can be indicated as xy/z×0.1 when the frequency of laser beams isset to x [Hz], the beam width of a laser beam in a minor axis directionis set to y [μm], and the movement speed of the stage is set to z[mm/sec].

A first semiconductor film 502 is formed over the substrate 501. Acrystalline semiconductor film manufactured by performing heat treatmentafter doping a catalyst metal element into an amorphous semiconductorfilm is used as the first semiconductor film 502. Note that the firstsemiconductor film 502 is not limited to the above-mentioned film, andan amorphous silicon film may be used.

Next, a second semiconductor film 503(503 a and 503 b) is formed byirradiating the first semiconductor film 502 with the first laser beam.

A frequency of a laser beam and a beam width of a laser beam in minoraxis direction are fixed, the movement speed of the stage on which thesecond semiconductor film 503 is mounted is changed, and hence, theoverlap ratio of the region irradiated with a laser beam may be adjustedto 70%. The second semiconductor film 503 is formed by irradiating thefirst semiconductor film 502 with the first laser beam in accordancewith a manner described above. In this way, a region 503 a irradiatedwith the first laser beam and a region 503 b not irradiated with thefirst laser beam are alternately formed in cycles in the secondsemiconductor film 503. The regions 503 a and 503 b are formed at thearea ratio of 7:3.

Then, a third semiconductor film 504 is formed by irradiating the secondsemiconductor film 503 (503 a and 503 b) with the second laser beam.

A frequency of a laser beam and a beam width in lengthwise direction arefixed, the movement speed of the stage on which the third semiconductorfilm 504 is mounted, and hence, the overlap ratio of the regionirradiated with a laser beam may be adjusted to 1000 to 1500%. The thirdsemiconductor film 504 is formed by irradiating the second semiconductorfilm 503 with the second laser beam in accordance with the above manner.According to this manner, the third semiconductor film 504 is irradiatedat 10 to 115 number of times at a given point with the second laserbeam. Therefore, a region 504 a irradiated with the first and the secondlaser beams, and a region 504 b irradiated with only the second laserbeam are alternately formed in cycles in the third semiconductor film504.

FIG. 2 shows a top view of a part of the third semiconductor film 504.It can be seen that the regions 504 a and 504 b are alternately formedin cycles in striped pattern.

As described above, an irradiation frequency of laser beams in theregion 504 a differs from that in the region 504 b. As a result, filmquality of the region 504 a differs from that of the region 504 b.

In the present embodiment mode, the overlap ratio is adjusted bychanging the movement speed of the stage; however, the overlap ratio maybe regulated by changing the frequency of the laser beam or the beamwidth of the laser beams. Further, the overlap ratio is not limited tothe above-mentioned value, and it can be changed properly. Furthermore,the energy density of the first and the second laser beams may bedifferent from each other, and can be regulated properly.

A catalyst metal element is removed from the third semiconductor film504 which is formed as described above by a known gettering method.

TFTs 520 a and 520 b comprising a semiconductor films 505 a and 505 b, agate insulating film 506, a gate electrode 507 are formed by a known TFTmanufacturing method by using the third semiconductor film 504(504 a and504 b) in which the catalyst metal element is removed.

A TFT 520 a formed by using a semiconductor film 505 a separated fromthe third semiconductor film 504. In addition, a TFT 520 b is formed byusing a semiconductor film 505 b separated from the third semiconductorfilm 504.

In the present embodiment mode, a TFT having a p-channel type singlegate structure is formed by using a known method for manufacturing aTFT. In addition to the TFT having a single gate structure, a TFT havingother structures such as a Lightly Doped Drain (LDD) structure may beformed. As for the channel type, it is not particularly limited, andn-channel type TFT may be manufactured, or both of n-channel type andp-channel type TFTs may be manufactured.

After manufacturing a TFTs 520 a and 520 b, a wiring 511 fortransmitting an electric signal to an interlayer insulating film 510 andthe TFT is formed, and a TFT array substrate is manufactured. Note thatactivation and hydrogen treating are performed after manufacturing theTFTs 520 a and 520 b.

Plural TFTs are formed over the substrate 501 by the above-describedmethod. The electrical characteristic of the TFT 520 a manufactured byusing the semiconductor film 505 a differs from that of the TFT 520 bmanufactured by using the semiconductor film 505 a. Therefore, theposition dependency of the on current value of TFTs arranged in theminor axis direction of the regions 504 a and 504 b has a periodicalposition dependency. The way of the repetition of ups and down in the oncurrent value is similar to the repeat of the region 504 a and theregion 504 b. Accordingly, the TFT array substrate in which theelectrical characteristic of plural TFTs arranged in the same directionas the minor axis direction of a laser beam fluctuates periodicallydepending on the each TFT's position can be manufactured.

Then, a first electrode of a light emitting element (any one of an anodeor a cathode), a partition layer (also referred to as a bump or a bank),a light emitting layer, and a second electrode of the light emittingelement are formed over the TFT array substrate by using a know methodand a known material. A display device provided with a light-emittingelement formed of a first electrode of a light emitting element, a lightemitting layer, and a second electrode of the light emitting element canbe manufactured.

Embodiment Embodiment 1

In the present embodiment, a method for manufacturing a display deviceof the present invention is described with reference to FIG. 3A to 8B.In this embodiment, a display device provided with a light-emittingelement as a display device is manufactured.

According to a method for manufacturing a display device of the presentinvention, a TFT array substrate in which the electrical characteristicof plural TFTs arranged in the same direction as minor axis direction ofa laser beam fluctuates periodically depending on the each TFT'slocation can be manufactured. A periodical striped pattern is generatedin a display image of a display device provided with the TFT arraysubstrate. Consequently, brightness unevenness due to a random stripedpattern can be visually reduced specially in the case of displaying awhole image with single brightness and a mono color (namely, under thesame electric signal) by utilizing a visual advantage that a periodicalpattern is difficult to be visually recognized as image unevenness. Adisplay device of the present invention can be manufactured easily andat low cost compared with one manufactured by the conventional techniquesince a particular technique and the like are not required to an opticalsystem of a laser apparatus, and a maintenance of a laser oscillator isnot required frequently.

A base insulating film 1501 a with a film thickness of from 50 to 100 nmand a base insulating film 1501 b with a film thickness of from 50 to100 nm are deposited over a substrate 1500. The base insulating films1501 a and 1501 b are formed for preventing impurity diffusion from thesubstrate 1500 to a semiconductor layer. In the present embodiment, alow alkali glass is used as the substrate, a silicon nitride film with afilm thickness of 100 nm as the base insulating film 1501 a and asilicon oxide film with a film thickness of 100 nm as the baseinsulating film 1501 b are deposited by a plasma chemical vapordeposition (CVD) method. In the present embodiment, the insulating filmis formed by two lamination layers; however, it can be one laminationlayer or at least three lamination layers provided impurity diffusioncan be prevented.

Next, a semiconductor film is formed over the base insulating film 1501b. The method of the semiconductor film is described as below.

An amorphous silicon film (not shown) with a film thickness of 55 nm isformed over the base insulating film 1501 b by a known formation method(a CVD method, a sputtering method or the like). Subsequently, nickel(Ni) is doped therein as a catalyst metal element, and heat treatment isperformed at 550° C. for 4 hours in order to form a crystalline siliconfilm 5002.

Then, the crystalline silicon film 5002 is irradiated with a first laserbeam to form a crystalline silicon film 5003 (5003 a, 5003 b). In thepresent embodiment, an excimer laser beam of a pulsed laser beam havinga frequency of 30 Hz, a beam width of 476 μm, and a energy density (aset value) of 529 mJ/cm² is used as the first laser beam. A stage onwhich the substrate 1500 comprising the crystalline silicon film 5002 ismounted is moved at the movement speed of 20 mm/sec, and the crystallinesilicon film 5002 is irradiated with the first laser beam. Thus, thecrystalline silicon film 5002 is irradiated with the first laser beam atthe overlap ratio of 71.4%. Accordingly, the crystalline silicon film5003 in which a region 5003 a irradiated with the first laser beam and aregion 5003 b not irradiated with the first laser beam are alternatelyand repeatedly formed at the ratio of around 71:29 can be formed. Notethat the first laser beam irradiation is performed in an atmosphereincluding 20% oxygen and 80% nitrogen. (FIG. 3B)

Subsequently, the crystalline silicon film 5003 is irradiated with asecond laser beam to form a crystalline silicon film 5004 (5004 a, 5004b). In the present embodiment, the same laser apparatus as the one usedwhen irradiating with the first laser beam is utilized. As in the casewith the first laser beam, an excimer laser beam of a pulsed laser beamhaving a frequency of 30 Hz, a beam width of 476 μm, and an energydensity (a set value) of 529 mJ/cm² is used as the second laser beam. Astage on which the substrate 1500 comprising the crystalline siliconfilm 5003 is mounted is moved at the movement speed of 1 mm/sec, and thecrystalline silicon film 5003 is irradiated with the second laser beam.Thus, the crystalline silicon film 5003 can be irradiated with thesecond laser beam at the overlap ratio of 14.3%. Accordingly, thecrystalline silicon film 5003 is irradiated approximately 14 times at agiven point. Note that the second a laser beam irradiation is performedin an atmosphere including 20% oxygen and 80% nitrogen. (FIG. 3C)

Therefore, a region 5004 a irradiated with the first and the secondlaser beams and a region 5004 b irradiated with only the second laserbeam are periodically and repeatedly formed in a crystalline siliconfilm 5004. As described above, a formation method of the crystallinesilicon film in the region 5004 a differs form that of the crystallinesilicon film in the region 5004 b. As a result, film quality of eachcrystalline silicon film becomes different. Note that crystallinedispersion of a minor degree compared with the film quality differencebetween the regions 5004 a and 5004 b occurs in each regions 5004 a and5004 b.

In the present embodiment, the first and the second laser beams arelinear shaped beams formed by using an optical system respectively. Andthe length in the minor axis direction of the beam is to be a beamwidth. Further, the first and the second laser beams come out from thesame laser apparatus, and the irradiation conditions of the oscillatoryfrequency, the beam width, the energy density (a set value) and the likeare same. FIG. 12 shows dispersion of energy density depending on theirradiation frequency of laser beams irradiated in the same irradiationcondition as the first or the second laser beam. According to this, itcan be seen that the energy density has extremely random dispersion tothe irradiation frequency.

FIG. 10A is a photograph of a sample substrate in which crystallinesilicon films 6002, 6003, and 6004 which are equivalent to therespective crystalline silicon films 5002, 5003, and 5004, respectivelyare formed by the same formation method as the one in 5002, 5003, and5004. After nickel (Ni) is doped therein as a catalyst metal element, acrystalline silicon film formed by performing heat treatment is to belocally irradiated with the first and the second laser beams. Thus, thecrystalline silicon film 6002 not irradiated with a laser beam at all,the crystalline silicon film 6003 irradiated with only the first laserbeam, and the crystalline silicon film 6004 irradiated with both of thefirst and the second laser beams are formed in the same substrate.Moreover, a crystalline silicon film 6005 irradiated with only thesecond laser beam is also formed.

The sample substrate is taken a photograph by irradiating the samplesubstrate with halogen light diagonally in a dark room. Therefore, thecatoptric light on the surface of the substrate appears as an image. Itbecomes lighter in the place having larger unevenness on the surface ofthe substrate on which the catoptric light is easily scattered, anddarker in the place having smaller unevenness on the surface of thesubstrate on which the catoptric light is hardly scattered.

Since unevenness is formed on the surface of the crystalline siliconfilm irradiated with the laser beams (the first and the second laserbeams), the difference in the unevenness causes the difference in theamount of the scattered light of the halogen light, thereby appearing aslight and shade in the image. Accordingly, the crystalline silicon film6002 is to be a dark image since it is not irradiated with the laserbeam and has a flat surface. Further, the crystalline silicon film 6003is to be a light image having a periodical striped pattern since aregion of the crystalline silicon film 6003 which is irradiated withfirst laser beam has unevenness. The whole surface of the crystallinesilicon film 6004 has unevenness since the whole surface of the film isirradiated with the second laser beam. Therefore, the whole surface ofthe crystalline silicon film 6004 has is lighter than that of thecrystalline silicon films 6002 and 6003. Further, the region irradiatedwith the first and the second laser beams differs from the regionirradiated with only the second laser beam in the unevenness of the filmsurface. And therefore, the difference of the unevenness appears as aperiodical stripe pattern. The crystalline silicon film 6005 isirradiated with only the second laser beam, and the condition of theunevenness in the surface of the film varies under the influence of theoutput dispersion of the second laser beam, and a random striped patternappears on the surface of the film.

As described above, the difference in the condition of the unevennessappears according to the difference of the laser irradiation manner. Inthe crystalline silicon film 5004, the region 5004 a differs from theregion 5004 b in the unevenness of the film surface according to thepresence or absence of the first laser beam irradiation.

In addition to an excimer laser as in the present embodiment, a pulsedoscillation type laser using YAG or YVO₄ may be used as a laser mediumfor the first and the second laser beams. In addition, the oscillatoryfrequency, the beam width, and the energy density of a laser beam arenot limited to the above mentioned value, and they can be properlyadjusted in view of the overlap ratio of each laser beam, the filmquality of the formed crystalline silicon film and the like. It is notobjectionable that the first laser beam differs form the second laserbeam in the condition of the energy density, or the like.

It is possible to form a crystalline silicon film in which a regioncrystallized with a laser beam and a region not crystallized with alaser beam are periodically and repeatedly formed as the crystallinesilicon film 5003 by using a continuous oscillation laser beam.

An amorphous semiconductor film such as amorphous silicon germanium(Si_(x)Ge_(1−x)(X=0.0001 to 0.02) can be used in order to form thecrystalline silicon film 5004 in addition to the amorphous silicon film.Further, the process in which the crystalline silicon film 5002 isformed by using a catalyst metal element is not indispensable, and thecrystalline silicon film may be formed by using the similar process tothe process for forming the crystalline silicon films 5003 and 5004after forming the crystalline silicon film. However, the formation ofthe crystalline silicon film 5002 as in the present embodiment haseffect of improving the orientation of the crystalline silicon film.With respect to the film thickness, it is not limited to the oneabove-mentioned value, and it can be properly changed. Furthermore,after the formation of the crystalline silicon film 5004, the surface ofthe film may be flattened by irradiating the crystalline silicon film5004 with a laser beam in the nitrogen atmosphere.

A thin oxide layer of 1 to 2 nm in thickness is formed on the surface ofthe crystalline silicon film 5004 by using ozone water. Then, anamorphous silicon film (not shown) having a thickness of 100 nm isformed thereon by sputtering. The catalyst metal element included in thecrystalline silicon film 5004 is moved to the amorphous silicon film andremoved (gettering) by heat treatment of furnace for 4 hours at 550° C.After the gettering, the amorphous silicon film which became useless(there is a case that the amorphous silicon film becomes crystallinesilicon film by the effect of the catalyst metal element aftergettering.) is removed by TMAH solution and further removed byhydrofluoric acid.

Semiconductor films 1502 a to 1502 d are formed in the region 5004 a byseparating from the crystalline silicon film 5004 after gettering. Atthe same time, a semiconductor film separated from the crystallinesilicon film 5004 is formed in the region 5004 b. In the presentembodiment, an element having a same structure is formed in the regions5004 a and 5004 b by the same process. Therefore, the element formed byusing the semiconductor film of the region 5004 b is not speciallyillustrated, and the description in the specification is also omitted.

An impurity doping (channel dope) may be performed in order to controlthe threshold value of the TFT before or after forming the semiconductorfilms 1502 a to is 1502 d. As the impurity for doping, boron, phosphorusor the like is used.

Next, a gate insulating film 1503 is formed so as to cover thesemiconductor films 1502 a to 1502 d. In the present embodiment, asilicon oxide film is formed to have a thickness of 110 nm by a plasmaCVD method. Note that other insulating films may be used in addition tothe silicon oxide film. The film thickness is not limited to theabove-mentioned value and can be changed properly in consideration ofthe dielectric constant, and the like.

A conductive film 1504 and a conductive film 1505 are laminated on thegate insulating film 1503. In the present embodiment, the conductivefilm 1504 are formed to have a thickness of 30 nm by depositing tantalumnitride (TaN) with sputtering and the conductive film 1505 are formed tohave a thickness of 370 nm by depositing tungsten (W) with sputtering. Amaterial used for forming the conductive films 1504 and 1505 are notlimited to tantalum nitride or tungsten as described above. And anelement selected from the group consisting of Ta, W, Ti, Mo, Al, Cu, Crand Nd, an alloy film or a compound material in which the above elementsare combined, or a semiconductor film represented by a polycrystallinesilicon film to which an impurity element such as phosphorus is addedmay be used for the conductive films. A material having higher adhesionto the gate insulating film is selected to the conductive film 1504 anda material having lower resistance in which ohmic value of approximately9 to 20 μΩ is obtained is selected to the conductive film 1505. (FIG.4A)

Then, the conductive films 1504 and 1505 are formed into the desiredshape by pattering and etching. First, resist masks having sloping sidewalls 1510 to 1513 are formed. Then, the conductive film 1505 is etchedby using the resist masks 1510 to 1513 as a mask, and the conductivefilm 1504 is formed by etching. The conductive film 1505 is manufacturedinto conductive films 1506 b, 1507 a, 1508 a, and 1509 a each of whichhas a taper angle of approximately 26° in its side wall. Moreover, theconductive film 1504 is also manufactured into the conductive films 1506a, 1507 a, 1508 a, and 1509 a each of which has a taper angle of 15° to45° in its side wall. (FIG. 4B)

The conductive films 1506 b, 1507 b, 1508 b, and 1509 b are selectivelyetched by using resist masks 1518 to 1521 as a mask. The conductivefilms 1506 b, 1507 b, 1508 b, and 1509 b are manufactured into theconductive films 1514 b, 1515 b, 1516 b, and 1517 b each of which hasalmost perpendicular side wall respectively. In this case, anisotropicetching which is anchored by perpendicular direction has to be used foretching. Also, the resist masks 1510 to 1513 which are used for etchingin the above conductive films 1504 and 1505 are directly used for theresist masks 1518 to 1521. The conductive films 1506 a, 1507 a, 1508 a,and 1509 a are not processed and left as the conductive films 1514 a,1515 a, 1516 a and 1517 a.

As described above, a gate electrode 1514 formed of the conductive films1514 a and 1514 b, a gate electrode 1515 formed of the conductive films1515 a and 1515 b, a gate electrode 1516 formed of the conductive films1516 a and 1516 b, and the gate electrode 1517 formed of the conductivefilms 1517 a and 1517 b are formed.

Next, low concentration n-type impurities are doped using the gateelectrodes 1514 to 1517 as a mask. In the present embodiment mode,phosphorus at the concentration 1×10¹⁷ atmos/cm³ is doped into thesemiconductor films 1502 a to 1502 d as low concentration impurities toform low concentration impurity regions 1522 a to 1522 d. The lowconcentration impurities doping is performed in order to form an LDD(Light Doped Drain) region for controlling off leak current of a TFT.The off leak current is changed by the doped impurities concentration.Therefore, the amount of the doping impurities is properly changed sothat the value of the off leak current does not exceed the regulation.In the present embodiment, phosphorus is used as an n-type impurity,however it is not limited and the other impurities may be used. (FIG.5A)

The high concentration n-type impurities are doped using resist masks1525 to 1527 and the conductive films 1514 b as a mask. The resist mask1525 are formed in order to cover the semiconductor film 1502 b and thegate electrode 1515, the resist mask 1526 are formed in order to coverthe one part of the semiconductor film 1502 c(the region which is to bean LDD region) and the gate electrode 1516, and the resist mask 1527 areformed in order to cover the semiconductor film 1502 d and the gateelectrode 1517. In the present embodiment, high concentration phosphorusof the 1×10²⁰ atmos/cm³ is doped into the region in the semiconductorfilm 1502 a over which the conductive film 1514 a is not formed, and theregion in the semiconductor film 1502 c over which the resist mask 1526is not formed. At the same time, low concentration phosphorus of 1×10¹⁸atmos/cm³ is doped into the region in the semiconductor film 1502 a overwhich the conductive film 1514 a is formed, thereby forming a source (ora drain) 1523 a, 1523 b including high concentration phosphorus, and alow concentration impurity region 1524 a, 1524 b including lowconcentration phosphorus. The difference of the blocking capacity towardimpurities being doped, between the region in which the conductive film1514 a is formed and the region in which the conductive film is notformed, is utilized. In the present embodiment, phosphorus is used as ann-type impurity, however it is not limited and other impurities may beused. (FIG. 5B)

Then, high concentration p-type impurities are doped using the resistmasks 1530 and 1531 and the conductive films 1515 b and 1517 b as amask. The resist mask 1530 is formed so as to cover the semiconductorfilm 1502 a and the gate electrode 1514, and the resist mask 1531 isformed so as to cover the semiconductor film 1502 c and the gateelectrode 1516. In the present embodiment, high concentration boron ofthe 1×10²⁰ atmos/cm³ is doped into the region of the semiconductor films1502 b and 1502 d over which the conductive films 1515 a and 1517 a arenot formed in order to form sources (or drains) 1528 a and 1528 b. Atthe same time, low concentration boron of 1×10¹⁹ atmos/cm³ is doped intothe region of the semiconductor films 1502 b and 1502 d over which theconductive films 1515 a and 1517 a are formed, thereby forming the lowconcentration regions 1529 a and 1529 b. In the present embodiment,boron is used as a p-type impurity, however it is not limited and otherimpurities may be used. (FIG. 5C)

As described above, TFTs 1550 to 1553 are manufactured by thecrystalline silicon film 5004 in the region 5004 a. The TFTs 1550 and1551 are the one for driver circuit, and the TFTs 1552 and 1553 are theone for driving a light-emitting element. As already mentioned, TFTshaving same shapes as the TFTs 1550 to 1553 which are formed by usingthe region 5004 b in the crystalline silicon film 5004 are manufactured.Note that a structure of a TFT and a method for manufacturing a TFTafter forming the semiconductor films 1502 a to 1502 d are not limitedto those illustrated in the present embodiment, and the others knownstructures or a methods may be used.

An interlayer insulating film 1532 is formed so as to cover a TFTmanufactured over the substrate 1500. In the present embodiment, theinterlayer insulating film is formed by silicon nitride oxygen (SiNO) of100 nm in thickness having hydrogen by a plasma CVD method. Note that itis not limited to the silicon nitride oxygen (SiNO), and otherinsulating films may be used. The film thickness is not also limited tothe above-mentioned value, and can be properly changed in considerationof the dielectric capacity.

In the next place, hydrogenation for terminating dangling bonds in asemiconductor layer is performed. In the present embodiment,hydrogenation is conducted by performing a heat treatment at 410° C. for1 hour in the nitrogen atmosphere. The hydrogen is released from aninterlayer insulating film 1532. In addition the above-mentioned method,the hydrogenation may be conducted by performing heat treatment in theatmosphere including hydrogen, or by using hydrogen plasma.

An interlayer insulating film 1533 is formed over the interlayerinsulating film 1532. In the present embodiment, the interlayerinsulating film 1533 is formed by applying acrylic resin of 0.8 μm inthickness. The acrylic resin is flat by itself, so the surface of theinterlayer insulating film 1533 is to be flat.

Further, an interlayer insulating film 1534 is formed over theinterlayer insulating film 1533. In the present embodiment, theinterlayer insulating film 1534 is formed by depositing the siliconnitride film of 100 nm by using sputtering. Note that the interlayerinsulating film 1534 has an effect of preventing impurities. (FIG. 6A)

Then, contact holes which reach to sources (or drains) 1523 a, 1523 b,1528 a, and 1528 b are formed by performing patterning and etching. Inthe present embodiment, the contact holes are formed by dry-etching theinterlayer insulating films 1532, 1533, and 1534 after pattering.

A wiring 1535 for transmitting an electric signal to each TFT is formed.The wiring 1535 is formed as below: forming the conductive film in whichtitanium of 100 nm in thickness, aluminum of 350 nm in thicknessincluding a few percentage of silicon, and titanium of 100 nm inthickness are laminated after forming contact holes, and performingpatterning and etching thereon. Note that a material having electroconductivity other than the one described here may be used for formingthe wiring. Furthermore, the lamination structure and the film thicknessmay be properly changed. (FIG. 6B)

An electrode 1536 of a light-emitting element having a contact area withthe wiring 1535 is formed. The electrode 1536 of a light emittingelement is formed as below: forming an amorphous ITO (indium Tin Oxide)film of 110 nm in thickness; performing patterning and etchingthereover; and baking it at 220° C. for 60 min. The etching of the ITOis performed using water solution including oxalic acid ((COOH)₂) in theconcentration of at least 5.0% at the water temperature of 45° C. sothat the wiring 1535 is not corroded. Note that the condition of thebaking for crystallizing an amorphous ITO film is not limited to the onedescribed above, and can be properly changed.

Next, an insulating film 1537 having an opening portion for exposing onepart of the electrode 1536 of a light emitting element is formed. Theinsulating film 1537 is formed by applying photosensitivity positivetype acrylic film of 1.5 μm in thickness, and exposing and developingthereof. The insulating film 1537, which is also referred to as anembankment, a bank, or the like, is provided for covering the wiring1535 and the edge portion of the electrode 1536 of a light emittingelement. Further, the insulating film 1537 functions as a partition walllayer for each light-emitting element. The insulating film 1537 has anedge portion having a round shape. In addition to photosensitivitypositive type acrylic, a resin material having self flatness such asphotosensitivity negative type acrylic, resist (both of positive typeand negative type can be used) photosensitivity polyimide(both ofpositive type and negative type can be used), or an inorganic materialcan be used for forming the insulating film 1537. (FIG. 7A)

FIG. 13 is a result showing on current characteristic of plural TFTsarranged in a line to the same direction as the minor axis direction ofa laser beam, namely to the is direction in which the crystallinesilicon films 5004 a and 5004 b are periodically and repeatedly arrangedin the TFT array substrate manufactured by the above described method.The measured TFTs are arranged at 189 μm intervals, and the design is tobe a channel length of 420 μm, and a channel width of 6 μm. The channelis to be a p-type channel. The plural TFTs are respectively referred toas the nth TFT by the arranged order. In FIG. 13, the drain current, inthe case that the gate voltage is 3V and the drain voltage is 5V, is tobe on current value. The on current value belongs to a saturation regionin VD-ID characteristic.

FIG. 13 shows that on current value of TFTs repeat higher on currentvalue and lower on current value, and fluctuates while having the periodby approximately three to four step (namely, approximately, 567 to 756μm). The repetition period in the crystalline silicon film 5004 isapproximately 666 μm (the value is obtained since the width of thecrystalline silicon film 5004 a corresponds to the beam width of thefirst laser beam). Thus, it would appear that the periodical change inthe on current value of a TFT by the step shown in FIG. 13 signifies theperiodical change of the film quality in the crystalline silicon film5004.

As described above, a TFT array substrate over which plural TFTs arearranged, in which an electrical characteristic under the same electricsignal of plural TFTs arranged in a line in at least one direction ofcolumns or rows periodically fluctuates depending on the position inwhich each TFT is formed, can be manufactured.

In the present embodiment, a TFT for driver circuit and a TFT fordriving a light-emitting element are manufactured in the same substrate.Therefore, when the on current value periodically fluctuates asdescribed above, the amplitude of on current value causes dispersion ofon current value to the TFT for driver circuit, and may disturb theoperation. Consequently, the amplitude of the on current value isproperly adjusted to the degree that does not affect the operationcharacteristic of TFT for driver circuit (in the range of operationmargin of a TFT for driver circuit). Note that the dispersion of oncurrent value includes dispersion of contiguous TFTs displaying thecharacteristic difference in the contiguous TFTs, and in-planedispersion displaying dispersion of the entire TFTs in the substrate.However, the dispersion of contiguous TFTs is specially considered here.The dispersion of contiguous TFTs in the TFT array substratemanufactured in the present embodiment is approximately 10%. This valueis reflected by the amplitude of the on current value which fluctuatesperiodically. The TFT for driver circuit is designed so as to drivewithout problems in the approximately ±10% dispersion. In addition, thepresent invention may not be applied to the place in which a TFT fordriver circuit is formed, and the TFT may be formed by using otherprocesses. It becomes possible by adjusting the irradiation position ofa laser beam and the like.

A method for manufacturing an organic compound layer 1538 over the TFTarray substrate manufactured as described above is described using FIG.7B.

First, baking for removing moisture remained in the TFT array substrateand pretreatment such as irradiation of ultraviolet radiation areperformed.

Next, CuPc with a thickness of 20 nm as a hole injection layer, α-NPDwith a thickness of 40 nm as a hole transporting layer, Alq₃ including0.3% of DMQD with a thickness of 37.5 nm as a light emitting layer, andAlq₃ with a thickness of 37.5 nm as a electron transporting layer arelaminated, and represented as an organic compound layer 1538.

Note that the material for forming organic compound layer and the filmthickness thereof are not limited to those described above, and theother known material may be used. Further, plural formation of organiccompound layers having various lamination structures, materials and thelike may be carried out for multicolor emission.

Then, an electrode 1539 of a light emitting element is formed. Theelectrode 1539 of a light emitting element is formed by lamination ofcalcium fluoride (CaF₂) and aluminum (Al—Li) including severalpercentage of Li.

As described above, a light emitting element 1541 in which the electrode1536 of a light emitting element, the organic compound layer 1538, andthe electrode 1539 of a light emitting element are laminated is formed.

Furthermore, a protection film 1540 for protecting a light emittingelement 1541 is formed. In the present embodiment, a silicon nitridefilm is formed by sputtering for forming the conductive film 1540. Notethat other materials such as DLC (Diamond like Carbon) may be used forforming the conductive film in addition to the silicon nitride film.

Furthermore, a sealant substrate and a Flexible Printed Circuit (FPC)are installed by a known method. In the present embodiment, adesiccating agent is installed in the sealant substrate.

As described above, a light-emitting device according to the presentinvention is manufactured.

In a light emitting apparatus of the present embodiment, light generatedin the organic compound layer 1538 is let in from the side of theelectrode 1536 of a light-emitting element. The light-emitting element1541 may be formed for letting in light from the side of the electrode1539 of a light-emitting element. In this case, a conductive film havinglight transmittance may be used for the electrode 1539 of alight-emitting element.

FIG. 8A is a top view of a light emitting device, and FIG. 8B is asectional view taken on line A-A′ of FIG. 8A. Reference number 2001represents a source signal line driver circuit shown by a dotted line;2002, a pixel portion; 2003, a gate signal line driver circuit; and2004, a sealant substrate. The inside surrounded by the sealantsubstrate 2004 and the sealant 2005 is an empty space.

Reference number 2008 represents wiring for transmitting signalsinputted to the source signal line driver circuit 2001 and the gatesignal line driver circuit 2003. The wiring 2008 receives a video signalor a clock signal from a flexible print circuit (FPC) 2009 which will bean external input terminal. Only the FPC is illustrated here, but aprint wiring board (PWB) may be attached to this FPC. The light emittingdevice referred to in the present specification is not only the body ofthe light emitting device but also the one attached a FPC or a PWB.

FIG. 11A is a photograph of display image in a light-emitting devicemanufactured according to the present invention. FIG. 11B is aphotograph of display image in a light-emitting device manufactured byusing a conventional technique. The display image is the one obtained byinputting the electric signal so that the display image is to be singlebrightness and a mono color, and displaying the signal. Here, the imageis displayed in the dark room and is taken the photograph.

According to FIGS. 11A and 11B, it can be seen that striped shapedisplay unevenness appears in the display image manufactured by aconventional technique; however, brightness unevenness is eliminated inthe display image manufactured in the invention.

Usually, luminescence brightness is changed relative to the differencein on current value of a TFT for driving a light emitting element in adisplay device provided with a light emitting element. In the case ofapplying the same electric signal to all the TFTs for driving a lightemitting element provided for the display device in order to displayingthe whole image with single brightness and a mono color, it easily andvisually recognized as display unevenness when the brightness ofcontiguous pixels is different at least 2%. Therefore, a display devicecapable of displaying 64 gradations requires having on current value ofa TFT for driving a light-emitting element wherein the dispersion ofcontiguous space is at most a few percentages. However, brightnessunevenness visually seems to be reduced in the display device of thepresent invention even the dispersion of contiguous space isapproximately ±10%. This is because when the same electric signal isapplied to all the TFTs for driving a light emitting element providedfor the display device, the periodical stripe pattern appears and it isdifficult to be visually recognized as the display unevenness in thedisplay of the present invention.

The less different the brightness between a stripe and a stripe situatednext to the stripe is, the less remarkable the striped shape is,therefore, the pattern can be visually recognized as a single image inthe periodical striped pattern. Further, in the case that stripedpattern having a stripe as thin as that can not be recognized, that canbe visually recognized as an monocolored image. Consequently, theirradiation condition of a laser beam, the movement speed of the stage,and the like are required to be considered so that the visual advantageis produced by the electrical characteristic of plural TFTs arranged ina line to the minor axis direction of a laser beam that is formed to alinear shape.

Embodiment 2

In the present embodiment, a method for manufacturing a display deviceof the present invention is described with reference to FIGS. 9A and 9B.

According to the method for manufacturing a display device of theinvention, a TFT array substrate in which the electrical characteristicunder the same electric signals of plural TFTs arranged in the samedirection as minor axis direction of a laser beam fluctuatesperiodically depending on the each TFT's location can be manufactured.In a display device manufactured of the TFT array substrate, randomgradation unevenness resulted from liquid crystal unevenness (unevennessresulted from nonuniformity such as a cell gap) and irradiation energyof a laser beam can be visually reduced.

First, a method for manufacturing a TFT array substrate is described. Inthe present embodiment, a TFT array substrate provided with TFTs for adriver circuit of n-channel type or p-channel type, and pixel TFTs ismanufactured.

The similar TFT for a driver circuit as the TFTs 1550 and 1551 which areillustrated in the present Embodiment 1 may be manufactured. The similarTFT as the TFT 1552 is used as a pixel TFT for a TFT driving alight-emitting element, and the similar TFT as the TFT 1553 is notmanufactured in the embodiment. Therefore, the similar process asEmbodiment 1 until the process for manufacturing TFTs may be used. Thepresence of the TFT 1553 may be adjusted by a photo mask. In addition, astructure of TFTs and a method for manufacturing TFTs after forming asemiconductor film is not limited, and other known structures andmethods can be used as in the case with Embodiment 1.

In the present embodiment, a process after the TFTs manufacturingprocess is explained with reference to FIG. 9A.

After manufacturing TFTs for a driver circuit 1650 (n-channel type TFT),1651(p-channel type TFT), and a pixel TFT 1652, an interlayer insulating1632 for covering the above mentioned TFTs is manufactured. In thepresent embodiment, the interlayer insulating 1632 is formed bydepositing a silicon oxynitride(SiNO) including hydrogen of 100 nm thickby a plasma CVD method. The silicon oxynitride is not limited to beused, and other insulating films may be used. The film thickness is notlimited to the above-mentioned value, either, and can be properlychanged in view of dielectric constant.

Next, hydrogenation for terminating dangling bonds in a semiconductorlayer is performed. In the present embodiment, hydrogenation isconducted by performing a heat treatment at 410° C. for 1 hour in thenitrogen atmosphere. The hydrogen is released from the interlayerinsulating film 1632. The hydrogenation may be conducted by performingheat treatment in the atmosphere including hydrogen, or by usinghydrogen plasma.

An interlayer insulating film 1633 is formed over the interlayerinsulating film 1632. In the present embodiment, the interlayerinsulating film 1633 is formed by applying acrylic resin of 1.6 μm inthickness. The acrylic resin has a flat surface thereon.

Next, a contact hole which penetrates the interlayer insulating films1632 and 1633 is formed.

A wiring 1634 for transmitting electric signal to each TFT is formed.After forming contact holes, the conductive film in which titanium of100 nm in thickness, aluminum including a few percentage of silicon of350 nm in thickness, and titanium of 100 nm in thickness are laminatedis formed, and then, patterning and etching is performed thereon,thereby, forming the wiring 1634. A material having electro conductivityother than the one described above may be used for forming theconductive film. Furthermore, the lamination structure and the filmthickness may be properly changed.

A pixel electrode 1635 having a contact area with the wiring 1634 isformed. The pixel electrode 1635 is formed as below: forming anamorphous ITO (indium Tin Oxide) film of 110 nm in thickness bysputtering; performing patterning and etching thereon; and baking it at220° C. for 60 min. The etching of the ITO is performed using watersolution including oxalic acid ((COOH)₂) in the concentration of atleast 5.0% at the water temperature of 45° C. so that the wiring 1634 isnot corroded. The condition of the baking for crystallizing an amorphousITO film is not limited to the one described above, and can be properlychanged.

As stated above, a TFT array substrate 20 according to the presentinvention is manufactured.

Next, after forming an orientation film 1640 a over the TFT arraysubstrate, a rubbing treatment is performed on the orientation film.

Then, a counter substrate 10 in which a light-resistant film 1634, apixel electrode 1644, and an orientation film 1640 are formed over thesubstrate 1641 is manufactured. Note that a color filter may be formedif necessary. A rubbing treatment is performed on the orientation film1640 b.

After the counter substrate 10 and the TFT array substrate 20 arelaminated together, an unnecessary part is cut off. Further, a liquidcrystal material 1645 is injected between the counter substrate 10 andthe TFT array substrate 20, therefore, the two substrates are sealedtogether. Note that, the TFT array substrate 20 and the countersubstrate 10 are sealed with a spacer 1646 interposed therebetween.Furthermore, a FPC, a polarizing plate, and a phase plate are installed.A known method may be adapted to the above-described process. Asdescribed above, a liquid crystal device according to the presentinvention is manufactured.

FIG. 9B is a top view of the liquid crystal display device manufacturedaccording to the present invention. A scanning signal driver circuit 902a and an image signal driver circuit 902 b are provided for theperiphery of a pixel portion 901. The driver circuit is connected withan exterior input-output terminal 904 with a connection wiring band 903.In the pixel portion 901, a gate wiring band extended from the scanningsignal driver circuit 902 a and a data wiring band extended from theimage signal driver circuit 902 a cross at matrix shape, thereby forminga pixel. A sealant 905 is formed outside of the pixel portion 901, thescanning signal driver circuit 902 a, the image signal driver circuit902 b, and a logic operation circuit 902 c over a TFT array substrate908, and inside of the exterior input terminal 904. The liquid crystaldisplay device has a FPC board 906 which is connected to the exteriorinput-output terminal 904, and the exterior input-output terminal 904 isconnected to the driver circuit respectively with the connection wiringband 903. The exterior input-output terminal 904 is formed of the sameconductive film as the data wiring band. A FPC 906 has organic resinfilms such as polyimide in which a copper wiring is formed, and isconnected to the exterior input terminal 904 with an anisotropicconductive bonding member.

Embodiment 3

In the present embodiment, electronic apparatus according to the presentinvention is described. A method for manufacturing a semiconductordevice according to the present invention does not require a particulartechnique and the like to an optical system of a laser beam, neitherrequire the higher frequency of maintenance of a laser oscillator inspecific. Therefore, the semiconductor device can be formed easily andcan be formed at lower cost compared with the one manufactured by theconventional technique. As a result, a display device using asemiconductor device of the present invention can be manufactured atlower cost. Further, electronic apparatus over which the display deviceis mounted can be also manufactured at lower cost, and the better imagecan be obtained. In addition, the display device can be applied to alight emitting device and a liquid crystal display device.

FIG. 14A is a display device, which includes a case 5501, a supportmedium 5502, and a display portion 5503. The present invention can beapplied to the display device having the display portion 5503.

FIG. 14B is a video camera, which is composed of a body 5511, a displayportion 5512, a sound input 5513, an operation switch 5514, a battery5515, an image receiving portion 5516 and the like.

FIG. 14C is a laptop personal computer, which is composed of a body5501, a case 5502, a display portion 5503, a keyboard 5504, and thelike.

FIG. 14D is a personal digital assistant (PDA) manufactured by applyingthe present invention, which has a body 5531 provided with a displayportion 5533, an external interface 5535, an operation button 5534, andthe like. And a stylus 5532 as an accessory for an operation is alsoprovided.

FIG. 14E is a digital camera, which is composed of a body 5551, adisplay portion (A) 5552, and an eye piece 5553, an operation switch5554, a display portion (B) 5555, a battery 5556 and the like.

FIG. 14F is a cellular phone manufactured by applying the presentinvention. The cellular phone includes a body 5561 for which a displayportion 5564, a sound output portion 5562, a sound input portion 5563,an operation switch 5565, an antenna 5566, and the like are provided.

According to a method for manufacturing a display device of the presentinvention, a display device provided with a TFT array substrate overwhich plural TFTs are arranged, in which the electrical characteristicunder the same electric signals of plural TFTs arranged in a line in atlease one direction of column or row fluctuates periodically dependingon the place in which each TFT is formed can be manufactured. Aperiodical pattern is generated in a display image of a display device.Consequently, random brightness unevenness, gradation unevenness can bevisually reduced specially in the case of displaying a whole image withsingle brightness and a mono color (namely, under the same electricsignal) by utilizing a visual advantage that a periodical pattern isdifficult to be visually recognized as display unevenness. A displaydevice of the present invention can be manufactured easily and at lowercost compared with the one manufactured by the conventional techniquesince a particular technique and the like are not required to an opticalsystem of laser apparatus, and a maintenance of a laser oscillator isnot required frequently.

1. A method for manufacturing a display device comprising: forming afirst semiconductor over a substrate; forming a second semiconductorfilm by irradiating the first semiconductor film with a first linearshaped pulsed laser beam while moving the substrate in a minor axisdirection of the first linear shaped pulsed laser beam so that pluralfirst regions irradiated with the first linear shaped pulsed laser beamare formed at periodical intervals; irradiating whole of the secondsemiconductor film with a second linear shaped pulsed laser beam inorder to form a third semiconductor film, wherein the plural firstregions irradiated with both of the first and the second linear shapedpulsed laser beams and plural second regions irradiated with only thesecond linear shaped pulsed laser beam are periodically and repeatedlyformed in the third semiconductor film.
 2. A method for manufacturing adisplay device according to claim 1, wherein the first semiconductor isa crystalline semiconductor film formed by adding a metal element intoan amorphous semiconductor film and performing a heat treatment.
 3. Amethod for manufacturing a display device according to claim 1, whereinthe first plural regions are irradiated with the first linear shapedpulsed laser beam plural times.
 4. A method for manufacturing a displaydevice according to claim 1, wherein the first plural regions and theplural second regions are irradiated with the second linear shapedpulsed laser beam plural times.
 5. A method for manufacturing a displaydevice according to claim 1, wherein a light emitting element is formedafter forming the third semiconductor film.
 6. A method formanufacturing a display device, comprising: forming a firstsemiconductor over a substrate; forming a second semiconductor film byirradiating the first semiconductor film with a first linear shapedpulsed laser beam while moving the substrate in a minor axis directionof the first linear shaped pulsed laser beam so that plural regionsirradiated with the first linear shaped pulsed laser beam are formed atperiodical intervals, irradiating whole of the second semiconductor filmwith a second linear shaped pulsed laser beam in order to form a thirdsemiconductor film, wherein a first region irradiated with both of thefirst and the second linear shaped pulsed laser beams and a secondregion irradiated with only the second linear shaped pulsed laser beamare periodically and repeatedly formed in the third semiconductor film;and forming at least first and second thin film transistor by using theplural first and second regions, respectively.
 7. A method formanufacturing a display device according to claim 6, wherein the firstplural regions are irradiated with the first linear shaped pulsed laserbeam plural times.
 8. A method for manufacturing a display deviceaccording to claim 6, wherein the first plural regions and the pluralsecond regions are irradiated with the second linear shaped pulsed laserbeam plural times.
 9. A method for manufacturing a display deviceaccording to claim 6, wherein a light emitting element is formed afterforming the first and second thin film transistors.
 10. A method formanufacturing a display device according to one of claim 6, wherein thefirst semiconductor is a crystalline semiconductor film formed by addinga metal element into an amorphous semiconductor film and performing aheat treatment.
 11. A method for manufacturing a display devicecomprising: forming a first semiconductor film over a substrate; forminga second semiconductor film having a first and a second periodicallystriped regions by irradiating a first laser beam to the firstsemiconductor film; and forming a third semiconductor film byirradiating a second laser beam to the first and the second periodicallystriped regions of the second semiconductor film, wherein the firstperiodically striped region is irradiated with the first laser beam, thesecond periodically striped region is not irradiated with the firstlaser beam.
 12. A method for manufacturing a display device according toclaim 11, wherein the first laser beam is a linear shaped pulsed laserbeam.
 13. A method for manufacturing a display device according to claim11, wherein the second laser beam is a linear shaped laser beam.
 14. Amethod for manufacturing a display device according to claim 11, whereinthe first and the second periodically striped regions are irradiatedwith the second laser beam at least twice.
 15. A method formanufacturing a display device according to claim 11, wherein the firstperiodically striped region of the second semiconductor film isirradiated with the first laser beam at least twice.
 16. A method formanufacturing a display device according to claim 11, wherein theirradiation of the first laser beam is performed in an atmosphereincluding oxygen.
 17. A method for manufacturing a display deviceaccording to claim 11, wherein the irradiation of the second laser beamis performed in an atmosphere including oxygen.
 18. A method formanufacturing a display device according to claim 11, wherein a lightemitting element is formed after forming the third semiconductor film.19. A method for manufacturing a display device comprising: forming afirst semiconductor film over a substrate; forming a secondsemiconductor film having a first and a second periodically stripedregions by irradiating a first laser beam to the first semiconductorfilm; forming a third semiconductor film by irradiating a second laserbeam to the first and the second periodically striped regions of thesecond semiconductor film, and forming a first and a second transistorsby using the first and the second periodically striped regions of thethird semiconductor film respectively, wherein the first periodicallystriped region is irradiated with the first laser beam, the secondperiodically striped region is not irradiated with the first laser beam,and wherein the first and the second transistors are arranged in theminor axis direction of the first laser beam.
 20. A method formanufacturing a display device according to claim 19, wherein the firstlaser beam is a linear shaped pulsed laser beam.
 21. A method formanufacturing a display device according to claim 19, wherein the secondlaser beam is a linear shaped laser beam.
 22. A method for manufacturinga display device according to claim 19, wherein the first and the secondperiodically striped regions are irradiated with the second laser beamat least twice.
 23. A method for manufacturing a display deviceaccording to claim 19, wherein the first periodically striped region ofthe second semiconductor film is irradiated with the first laser beam atleast twice.
 24. A method for manufacturing a display device accordingto claim 19, wherein the irradiation of the first laser beam isperformed in an atmosphere including oxygen.
 25. A method formanufacturing a display device according to claim 19, wherein theirradiation of the second laser beam is performed in an atmosphereincluding oxygen.
 26. A method for manufacturing a display deviceaccording to claim 19, wherein a light emitting element is formed afterforming the first and second thin film transistors.